Underlay Beneath Shingles
(1) Except as required in Sentence (2), when underlay is used beneath shingles, it shall be,
(a) asphalt-saturated sheathing paper weighing not less than 0.195 kg/m², or
(b) No. 15 plain or perforated asphalt-saturated felt.
(2) Underlay used beneath wood shingles shall be breather type.
Article 9.26.6.1. Ontario Regulation 332/12 Building Code, Information published by oncodes.ca for educational purposes only.
Source : Canada Mortgage and Housing Corporation (CMHC)